Aerosol containers are a common and popular means for the delivery of such diverse materials as spray paint, hair spray, lubricants, and the like. The product is loaded into the container, along with the propellant. The propellant is a liquid with a high vapor pressure, which provides the pressure for discharging the product. Alternatively, compressed gas may be used as the pressurizing medium. Aerosol containers, such as cans, are commonly pressurized to approximately 70 psi at room temperature which enables the contents to be expelled in a controlled release.
Aerosol containers currently in use are metal, of a three-piece construction or a two-piece construction. The three-piece containers consist of a seamed side wall, an outwardly domed top wall, and an inwardly domed bottom wall. The top and bottom walls are fastened to the cylindrical side wall by a mechanically formed double seam, with a sealing compound incorporated into the seam. In the two-piece containers, one end and the side wall are made in one piece by a forming step.
The shift in 1979 from halogenated hydrocarbons as the propellants requires improved aerosol containers capable of withstanding increased internal pressures. This, however, increases the potential danger if the container bursts, resulting in a rocketing reaction of the container.
It is therefore desirable to have a higher pressure aerosol container vent its pressurized contents rather than violently burst. The controlled vented release of the aerosol container contents, prior to achieving a pressurization that could cause explosive rupturing of the container, will reduce or avoid the dangers due to bursting of an aerosol container.
The introduction of artificial weakness into aerosol containers has recently had limited commercial production application. U.S. Pat. Nos. 3,850,339, issued Nov. 26, 1974 to Kinkel, 4,513,874, issued Apr. 30, 1985 to Mulawski and 4,588,101, issued May 13, 1986 to Ruegg disclose devices of this nature. These weaknesses can be broadly characterized as scores in the metal that are intended to locally fracture the material when a specific pressure range is reached or a specific over pressurization event occurs, such as to outwardly buckle the dome or the bottom end. These pressure release mechanisms are highly dependent on the manufacturing processes and controlled scoring of the metal. For the weakened area to fracture at the proper pressure, the tolerances of the manufacturing process must be closely and consistently controlled.
Further, U.S. Pat. No. 3,680,743, issued Aug. 1, 1972 to Reinnagel teaches that surface scoring methods for pressure venting have not proved reliable because material thickness tolerances do not allow for accurate scored thickness control.
U.S. Pat. No. 5,249,701, issued Oct. 5, 1993 to the present inventor taught an aerosol can with a plurality of interrupted welds or bonds between the end wall and the side wall of the can, whereby the failure of the can could be directed to occur at a location between the welds or bonds. That design works well under hydraulic conditions, or for cans which are full. However, for almost-empty cans, and partially-filled cans which are placed in a fire, the venting does not release the pressure quickly enough.
Therefore, it would be desirable to have a container design in which the container can withstand internal pressurization up to about 400 psi, or more, and which can safely vent said pressure in a non-explosive manner.